seaducer

Hello all, My name is Drew, and although I have had some classes on engines as well as reading the relevant posts here I still have some questions. I have an MDS .40, which appears to be a ringed engine (came mounted on an Extra EZ RTF). The "ring" is a darker metal at the top of the piston, not a removable ring like in a 4 stroke, the manual describes an ABC as the piston being all the same color, or 1 peice of metal, so mine with the stripe would be ringed? I can't tell from the 15 or so words in the manual. The manual also says to preadjust the two valves all the way in (CW) then back out (CCW) 2 1/2 turns and run 3 or 4 tanks this way. I have noticed some problems however... Adjusted this way I can't start the engine, I have the low speed valve set this way, but have had to turn the high speed needle all most all the way out to start, then I can bring it back in, and once the engine warms up I can start with these settings. Since there is no other info on breaking in the engine I have done the following for its first tankfull:
As soon as the engine starts I have removed the battery, and after 2 or 3 minutes at low idle I have been increasing throttle for 15 to 30 seconds, working the engine up incrementally (sp?). The engine usually dies at 3/4 throttle, though at times i have had it at the max setting. It runs smooth at all times at low idle, and for the most part accelerates smoothly, when it dies it drops rpm's quickly but smoothly, almost no stutter until it finally goes.

From some posts and an old book I gather my impression of "out" and "in" are backwards? Also, I have read on some other posts that I should only be able to run the engine with the battery attached, as it should be so rich it would stall otherwise. Would anyone with a well broken in and good performing MDS comment on that? I am afraid my manual is rather brief and not conclusive. Any info or websites would be appreciated. My flight skills are bound to handicapped as it is, a well tuned engine would help. At the moment I am on my own with this, no clubs in my area are taking on new pilots at this time.
TIA, Drew

Homebrewer

My Feedback: (8)

I may be wrong but the MDS .40 is ABC (ringless) and doesn't have a piston ring. I know that if an ABC engine is run repeatedely too lean and overheated that a dark black band on top of the piston will form. Is this what you see?

Scorpionjack

Drew;
Thats typical of an MDS, The MDS is overheating. If you have what you say your Low idle screw adjusted so it's idling fine and your engine is running at high fine, until it starts to overheat. This is what your seeing, as the engine overheats the engine will slowly start to loose Rpm's and finally quit. It's going to take alot of fuel for you to get to a point where the engine doesn't overheat anymore. If you are using an OS #8 plug take it out, go to the hobby shop and get a cooler plug. The MDS is a finicky motor until it's broke in and that will take about 2 Gallons.

Being that it's a 40 get a 10 X 6 prop on it, the MDS runs good on 15% Omega/Coolpower fuel. make sure whatever fuel you use is 18%-20% Oil content as this will help also with your cooling problem. Carb set screws loosen them and push down on the carb as you re-tighten them just to make sure you have no leaks. Close the High end Needle and open it to the recommended manufactures position and maybe another 1/2 turn open. If you have a Tach then run the Engine at a Slobbery rich run. Don't start moving the throttle until it will go through two tanks without overheating and stopping. Just let it run, When the engine runs out of fuel see if you can touch the head without Burning your fingers off. A little thing I use to do is hook up a Gallon of fuel and just let it run. When it can go through a gallon without shutting down and it throttles up and down to idle. It's ready for the field and your plane.


Hope this helps.

Hobbsy

My Feedback: (102)

Drew, I bought that same combination of plane and engine about three years ago, what appears to be a ring is a groove around the piston for oil to collect in. I solved the problem you're having by putting my Fox .46 ABC on the plane so I could break the engine in later. The Fox flew the plane so well I never put the MDS back on until I sold the plane. But I did eventually get the engine to run very well. It will never turn anything bigger than a 10x6.

Cactus.

My Feedback: (1)

these engine only seam to run on castor fuel because it hides all the problems with them, they have carbs ALL!!! over the engine.
take the carb out and run some sealer round the base, then jam it in TIGHT!
Then take the main needle out and put 1/8th" fuel tube over it and screw it back in.
make sure the back plate is tight.
The bottom end needle cant effect the top end when its running, so screw it most of the way in, having it flush with the rest of the fittings seams to be about right, but my 38 is as tight in as it will go, ( those extra carbs work well )
next, have the main needle about 1.5-2 turns out and fire it up, ( makes sure your plug is fine first )
Get the engine running full speed ( ! lol ) and if your fuel has castor make sure your gumming up your plane still from the exhaust, dont run it too lean, you want smoke out the back. our fuel is very clean and dosnt help these engine with their fudge conrods.
once you have the top end set, idle it back, keep it there for 15 seconds or so, if it starts to die, pinch the fule line, if it improves screw in the nedle 1/4 turn, if it cuts, takes it out 1/8th of a turn, keep doing this till you get the best pick up, after this dont play with the bottom end again, its all on top now.
that should help, if not, the best cure for this is a full pipe & 6" prop www.rcflyers.fsnet.co.uk then look for the movie links for the 30,000 rpm MDS

seaducer

Hello all, thanks for the info. Some of the things I left out, (hard to believe I forgot something, being a newbie and all ) the fuel is S&W brand, the sticker says it is 15%. The oil is castor AND synthetic. I don't "think" the ringing on the piston is from overheating, unless it was a very clean rebult, I looked before I attempted to start it, as per the manufacter's instructions. I think of a piston ring as being removable, and this appeared to be either a darker band on the piston or a blend of two different metals.

It does have a 10x6 prop on now, with a 10x7 waiting for later. The glow plug was preinstalled with a note that it is designed for breakin and should be replaced before I start to fly.

I hope this clarifies some things, and will try to follow all the advice so far and hope for the best. Worst case I'll go buy a new engine and chock this up to a learning experience.

Thanks again and please let me know any new ideas...

Drew